Fast and efficient piezoelectric actuation of self-injection locked photonic integrated lasers

Ultra-low-noise lasers with frequency tuning capabilities are essential for precision applications including coherent LiDAR, distributed fiber-optic sensing, and optical metrology. Photonic integrated self-injection locked (SIL) lasers have emerged as a compelling platform for achieving fiber laser-level coherence in a compact form factor, in part thanks to the frequency agility granted by the monolithic integration of piezoelectric actuators on chip. Nonetheless, the adoption of these frequency-agile lasers has been limited by the tradeoff between the efficiency and intrinsic linearity of the piezoelectric frequency tuning mechanism. Here, we present a novel approach to realize highly linear, fast and efficient frequency tuning of photonic integrated SIL lasers with piezoelectric actuators. We introduce a dis-aggregated actuator architecture in which the spiral resonator waveguide is arranged into multiple coils to maximize overlap with the piezoelectric stress field, increasing the tuning range and reducing the chirp non-linearity. We further showcase the implementation of piezoelectric actuators fabricated in aluminum scandium nitride (AlScN), which enables an improvement in piezoelectric actuation efficiency by about three times compared to identical designs based on aluminum nitride (AlN). The combination of the dis-aggregated actuator design with AlScN piezoelectric films achieves a tuning efficiency exceeding 35 MHz/V on unclamped chips and 18 MHz/V in a fully packaged device, almost an order of magnitude higher than previous state-of-the-art implementations. The packaged SIL laser demonstrates continuous and mode-hop-free frequency chirps exceeding 1.8 GHz with only 0.39% RMS nonlinearity, alongside sub-hertz intrinsic linewidths and integrated linewidths of approximately 1.3 kHz at 100 ms.